B - Eddy‘s AC難題

#include<bits/stdc++.h>
#include<algorithm>
using namespace std;
#define ll long long
ll c(ll n, ll m)
{
  ll a = 1;
  ll b = 1;
  for(ll i = 1; i <= m; i++)
  {
    a = a*(n-i+1) / i;
  }
  
  return a;
}
int main()
{
  ll n;
  while(~scanf("%lld",&n))
  {
    ll ans = 0;
    for(int i = 2; i <= n; i++)
    {
      ans += (i-1)*c(n,i);
    }
    printf("%lld\n",ans);
  }
}